Pregnancy associated recrudescence in murine malaria (Plasmodium berghei).

Depending on the strain, a variable proportion of mice solidly immune to the rodent malaria parasite Plasmodium berghei developed a recrudescence during pregnancy that was either transient or lethal. Recrudescence was not observed in all mice, and the rate was lower in gravida II as compared to gravida I mice. On the other hand a proportion of the mice that did not develop recrudescence exhibited a pregnancy associated clearance of persisting parasites in immune mice (premunition-sterile immunity), being more pronounced in gravida II than gravida I mice. Development of the mechanism of enhanced clearance is apparently parasite dependent. Enhanced clearance was manifest until day 4 of pregnancy. Pregnancy associated immunodepression was observed most strongly between day 4 and 16 of pregnancy, when the highest rates of recrudescence and associated mortality were found. Immunodepression apparently disappears at the end of pregnancy or shortly after parturition.